牛血清白蛋白初级团聚体分散体在多价反离子作用下的再稳定性和分形结构

Reentrant aggregation and fractal structure of bovine serum albumin pre-aggregates in dispersion induced by multivalent counterions

动态光散射的研究发现,牛血清白蛋白初级团聚体(BSA-PAs)的分散体在三价反离子钇离子(Y3+)作用下,团聚出现再稳定现象,即反离子浓度较低时BSA-PAs团聚速度较慢,增大反离子浓度团聚速度加快,再进一步增加反离子浓度其团聚速度反而又变慢了。经分析,BSA-PAs在高离子浓度下的再稳定性现象是由于过多的三价反离子与BSA-PAs表面结合导致表面偶极子增加所产生的短程排斥性水合力所致。小角光散射仪的静态光散射(SLS)和透射电镜(TEM)测试结果表明BSA-PAs团聚体在低和高反离子浓度时生成结构疏松的纤维状团聚体,在中间浓度时生成结构致密的球形团聚体,SLS和TEM进一步验证了高离子浓度时短程水合力的产生。这种短程水合力只在蛋白质带电或极性区域产生,它只能保护这些区域以免团聚发生,却不能保护两端的疏水性区域,所以BSA-PAs两端在反离子诱导团聚时相互连接生成纤维状团聚体。

Bovine serum albumin pre-aggregates in dispersion undergo a reentrant aggregation phenomenon upon adding trivalent counterion Y3+found by dynamic light scattering experiment,i.e.the aggregation of BSA-PAs is very slow at low counterion concentration,and it increases as the counterion concentration increases,while aggregation decreases as counterion concentration further increases.This reentrant condensation phenomenon is attributed to the short-ranged repulsive hydration force originating from increased dipoles generated by excess multivalent counterion binding.Small-angle light scattering and TEM(transmission electron microscope)results indicate that the incompact filamentous aggregates are formed at low and high counterion concentration,and the compact globular aggregates are formed at intermediated counterion concentration,which further supports the exist of hydration force at high counterion concentration.Hydration force occurs mainly on charged or polar patches of protein to protect it from aggregating;the aggregation of the filamentous BSA-PAs at hydrophobic patches at the two ends is still possible.